1. Field of the Invention
This invention relates to material storage and transfer facilities for bulk granular and powdered material storage. More particularly, the present invention relates to an improved crescent shaped auger cover that functions as both the auger cover and the structural support for an elongate material reclamation mechanism.
2. State of the Art
Many granular and powdered bulk materials require a controlled storage environment and unique handling profile during loading and unloading in storage areas. For example, grain, portland cement, fly ash, dry fuels, and other such commodities must be totally enclosed and protected from the elements when stored. However, the total enclosure of bulk materials limits convenient access for retrieval, making quick and complete reclamation difficult. Although movable roofing permits direct use of scoop shovels and buckets to raise the material to nearby trucks or railcars, such facilities and methods are labor intensive and require a significant capital investment for equipment and special construction of buildings.
There are many well known methods for the storage and retrieval of such materials. One method that has gained widespread popularity in recent years is the use of dome structures for storage. Free-standing dome structures, such as disclosed in U.S. Pat. No. 3,456,818, are extremely strong and space efficient, requiring a minimum of materials to obtain a large volume of enclosed space. They are also relatively inexpensive to construct as, for example, by thin-shell concrete balloon forming methods.
Additionally, reclamation of materials from an enclosed storage location may present significant challenges due to the nature of the material. For example, dry portland cement settles and compresses when stored, creating a compact and dense mass that can be difficult to remove. If one attempts to remove this material by a front-end loader through lateral doors at the base of a storage enclosure, the compressed cement may not readily collapse with removal of under-supporting material, allowing the creation of a sizable cavern within the material. This cavern could collapse suddenly, with disastrous results.
To solve these sorts of problems, automated reclamation devices for use within domed material storage structures have been developed. For example, U.S. Pat. No. 5,449,263 and prior patents disclose a free-standing dome storage structure having a mechanical reclaimer installed therein. Such a system is shown in FIG. 1. These reclaimers typically comprise a rotating vertical column 16 in the center of the dome storage structure 10, with one or more elongate material transfer mechanisms 40 and 41 attached thereto. These transfer mechanisms are necessarily shorter than the radius of the dome so as not to contact the inside surface of it. The transfer mechanisms typically employ auger devices 17 and 18 to move material, and are usually attached to a bridge type structure that is attached to the bottom of the column via a hinge 42 at their proximal end, and connected at their distal end to the top of the column via a cable 61 and winch device. The column 16 is rotated by a drive motor 60 located at the top of the column, with auger drive motors 62 positioned at the distal ends of the transfer structures. The cable 61 and winch mechanism allows the transfer structures to be selectively raised or lowered to contact the surface of the stored material.
The domed storage structure is typically filled via a conveyor 12 or similar transport mechanism that drops material into the dome through an opening 13 in the top center. Upon filling, the center column and transfer mechanism are designed to be buried in the stored material with the elongate transfer bridge retracted to an upright position as shown. When the material is to be reclaimed, a sufficient quantity of material is removed from the center of the dome by some means that allows pure gravity flow of the material into an outlet opening 19, such as by means of air jets upwardly directed from the bottom center of the dome. Then the transfer bridge structures 40 and 41 are lowered to the material surface, and as the column slowly rotates about its central axis 22, the augers sweep and drag the stored material toward the bottom center of the interior of the dome in a gradually declining conical motion, where, at the base of the column, some means is employed to gather the material and transport it under the floor of the dome.
The transfer bridge structures currently known and depicted in FIG. 1 present several drawbacks that have not been solved in the industry. First, the open truss design provides many flat surfaces upon which granular or powdered material may settle when the storage structure is filled. As the material settles, a significant load which should be borne by the floor of the structure is instead imposed upon the transfer structure, and thence upon the center column and its foundation. Such loads increase the size, complexity, and cost of construction of the center column and related structural elements. Second, conventional transfer structures expose a large portion of the auger blades, which, when in a relatively upright position, also provide a large surface on which material may settle and impose loads on the center column. Third, the open truss design is bulky and cumbersome. With the configuration shown in FIG. 1, it is not possible to retract the transfer bridge or bridges to a fully upright position because of interfering structure. It would be desirable in the industry to have a granular or powdered material reclamation mechanism for a domed reclamation enclosure that more completely enshrouds the auger blades and provides a more smooth exterior surface so as to reduce the vertical loads imposed on the center column, and which also has a smaller structural cross section so as to weigh less and occupy less space inside the enclosure.